Sulfamethoxazole Detection in Milk Using a Carbon-Based Printed Electrode: Enhanced Selectivity and Response Stability by Pulse-Amperometry

A simple, low-cost, and lab-made carbon-based electrode was developed for the fast and selective determination of sulfamethoxazole (SMX) in milk samples, requiring only minimal sample preparation (dilution in supporting electrolyte). A custom-made conductive ink (composed of glass varnish, graphite, acetone) was applied to a plastic surface to fabricate a flow-through amperometric sensor integrated into a portable Batch Injection Analysis (BIA) system. This method enhanced selectivity and reduced electrode contamination. The optimized pulsed amperometric waveform conditions included two detection pulses (+1.0 V and +1.3 V) and two cleaning pulses (+1.5 V and −1.5 V), resulting in a linear response from 1.0 to 20.0 μmol L −1 , with a detection limit of 0.31 μmol L −1 . The stability and reproducibility of the method were confirmed, exhibiting low relative standard deviations (RSD ≤ 8.3%). The system exhibited excellent recovery for spiked milk samples at concentrations of 5.0 μmol L −1 (68 ± 7%), 10.0 μmol L −1 (103 ± 7%), and 20.0 μmol L −1 (115 ± 7%), demonstrating high accuracy and minimal matrix interference. This approach offers a rapid, accurate, and reliable method for the analysis of complex samples, particularly for onsite detection of SMX in milk.